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Auto ISO and flash on the Nikon D7000, D5100, D3100 etc.

Summary: Newer Nikon DSLR cameras seem to choose unnecessarily high ISO values when using a flash in combination with auto-ISO – specifically in “P”, “A” and “S” mode. I have verified this issue for the Nikon D7000 and the D3100, and from forums I deduce that it also goes for the D5000, D3000, D5100 and D300s.

Auto ISO on Nikon’s DSLRs has gotten confusing

Auto ISO is a very useful feature found on many modern digital cameras. Nikon has been offering it for more than 6 years now, but they greatly surprised me by subtly changing the way it works in the D7000 (which I own). With “changed” I mean that they made it confusing and counter-intuitive.

The idea of Nikon’s auto ISO is simple enough: you set your default (minimum) ISO, a minimum shutter speed, and a maximum ISO.

As long as there is enough light the camera will use the minimum ISO.

As the illumination changes the camera will adjust the aperture and/or shutter speed (depending on whether you are in the P, A or S mode) to maintain correct illumination

When the light drops so low that the camera needs to use a slower shutter speed than the specified minimum it will raise the ISO while keeping the shutter speed on this limit.

When the maximum ISO value is reached the camera won’t raise it further but instead will again lower the shutter speed beyond its set minimum limit.

This is how it worked on my old Nikon D80, and how it still works on the D7000 as long as you don’t use flash. So far, so good.

But what happens if we use either the built-in or an external flash? It used to do what one would expect:

The flash (pop-up or external) adds extra light and the camera treats this extra light the same way it does natural light. Thus the camera reverts to its base ISO setting unless the flash is unable to provide the required light, in which case the ISO is increased to no more than the maximum auto-ISO value.

If the slow-sync flash setting is used the camera exposes for the scene as if the flash isn’t used, but also fires the flash. This is nice if you want to mix ambient background light with a flash-lit foreground.

But these days (with the D7000, D5100, D3100 etc.) Nikon does some strange things

The built-in flash is treated differently than a hot-shoe mounted flash (such as the Nikon SB600)

With popup flash the ISO is raiseduntil the ambient light (alone) is enough to properly expose the scene using the preset minimum shutter speed, or until the maximum ISO is reached. Much like in “slow sync mode”.

When a hotshoe-mounted flash is used, the ISO is raised to four times (4x) the specified ISO value unless the flash cannot provide enough light in which case the ISO is raised even further.

Note that although in these small
photographs you can’t see the noise
caused by very high ISO values, it
is very visible in the full size photographs.

“Auto” mode. Built-in flash. ISO 800, 1/60, F2.8

“Auto” mode. Hot-shoe flash. ISO 800, 1/60, F4.0

“P” mode. Built-in flash. ISO 3200, 1/200, F7.1

“P” mode. Hot-shoe flash. ISO 640, 1/200, F6.3

“P” mode. Built-in flash (“slow sync”). ISO 3200, 1/10, F7.1

“P” mode. Hot-shoe flash (“slow sync”). ISO 640, 1/2, F6.3

In the above example you see a number of odd things:

In P (Program) mode, the camera inexplicably chooses a small aperture (F6.3 or F7.1) when the flash is used – even in combination with “slow sync” flash. This leads to unnecessarily long shutter times and high ISO values.To me it makes no sense for the camera to use F7.1 in slow-sync mode if this requires ISO3200 at 1/10 second. This carries a huge risk of camera shake (blurry images) and has guaranteed noise – what for? The same lighting could be achieved with ISO 1600 and 1/30s by only changing the aperture to F2.8 – which was available with this lens!

In P mode, the ISO value chosen by the camera depends on whether the built-in or hot-shoe mounted flash is used. In the former case the ISO is limited by the max ISO, in the latter case by four times (4x) the base ISO.

The Auto mode seems to do the most sensible thing – it uses the available large aperture of the lens in combination with mid-range shutter and ISO values. But this mode cannot be controlled in any way.

The observed behaviour was not significantly influenced by the metering mode (spot / centre weighted / matrix) or whether “balanced” (flash mode) lighting was used or not.

Ken Rockwell partly figured this out but only describes the case for a hotshoe mounted flash when a base ISO of 100 is used. Surprisingly not even the D7000’s manual properly explains this unexpected behaviour; on p103-104 it states “ISO sensitivity is adjusted appropriately when the flash is used” and that “ISO sensitivity may be raised automatically when auto ISO sensitivity control is used in combination with slow sync flash modes“. But as I just stated, this is actually a description of how it used to work on Nikon’s older cameras, and precisely what goes wrong on the D7000. Googling it yielded few explanations (until this blog post, at least).

The big problem with the new auto-iso is that it now often happens that the D7000 unnecessarily reverts to a noisy high-ISO setting in combination with a weak flash setting where the flash is perfectly capable of providing enough light to use a low ISO. And even with the newest cameras that feature great low-light sensitivity, ISO still matters.

ISO matters: Cropped from ISO 100 photo.

ISO matters: Cropped from ISO 3200 photo.

In the days of analog cameras you could use a “fast” (high ISO) or “slow” (low ISO) film. Fast films were more sensitive to light but also more “grainy” (noisy). With digital cameras the ISO value can be changed with the push of a button. With a higher ISO value you increase signal amplification, thereby needing less light to make a photograph. Just as with film this comes at the cost of noisier images and less dynamic range.

I understand that this feature might sometimes improve photos by balancing ambient and flash light, reducing the “deer caught in headlights” look. But that was already covered by the slow-sync mode. In some cases there now seems to be little or no difference between normal and slow-sync pop-up flash modes. This is sort-of understandable in the bottom-range D3100 which has no slow-sync mode anyway, but this is not what I expect from an advanced camera like the D7000. Worst of all, Nikon made the auto-ISO system so confusing and badly documented that we are left with unexpected noisy photographs where they were not intended.

I know of two ways to work around this, but these are both clunky:

Workaround 1: Set the built-in flash to Commander mode and TTL in the sub-menu

Set the built-in flash (setting e3) to “Commander” mode, then in the accompanying sub-menu to TTL mode. This prevents auto-iso from raising the ISO, but you have to live with the longer preflash sequence (since the camera thinks that it needs to control an external flash)
OR

Disable auto-ISO whenever you want to use the flash. This can be made more convenient by putting auto-ISO settings at the top of “my menu” and assigning the customizable fn-button to the top of “my menu”. But this remains a cumbersome solution and forces you to remember changing the iso setting dependent on flash usage – exactly the kind of task loading auto-iso is supposed to solve.

I want to see Nikon do the following (firmware update, anyone?):

to use a more sensible and/or comprehensible approach and using larger apertures in “Program” mode if that can lower the required ISO

to clarify or remove the mysterious distinction between the way auto-ISO works with built-in vs. external flash

Overall, the camera shows just how overextended the current Nikon UI design has gotten. You will be hit by something that slows your shooting (or makes you miss a setting) someday, which is not what we want in a camera of this caliber. The details are getting rough-edged in so many areas that they won’t survive another expansion of capability, in my opinion.

In the 3 years since that review was written we have seen that the typical Nikon mid-range DSLR user interface did survive another generation, and still groans and creaks under the weight of feature creep.

(Disclaimer: I am not implying that Canon or any other manufacturer does this better. Only that I think that Nikon should do this better)

43 comments

Ken

It’s nice to know there’s someone else on the planet besides Ken Rockwell who recognizes this as a problem.

I “upgraded” to the d3100 from the d40. With the d40, I could set iso to auto and be relieved of that detail. Now I must ADD another detail into the mix (making sure I modify iso if I’m using flash).

I think the d40 was a GREAT camera. Everything just worked. The d3100 has better resolution, but seems to fall short when it comes to getting out of my way while I shoot.

Hi Ken
I still own a D80, which is a great old camera. I’d say that all the modern improvements outweight the negatives. I’d rather use a D3100 than a D40 due to the faster operation, better low light ability, availability of live view, etc. If one understands the ISO behaviour one can work around it. But yes, it’s confusing and annoying.

I have the D3100, I had to double check before commenting, but it has slow sync and slow sync red eye too. Maybe this was added in the only firmware update that came out so far.

I use an SB-600, and I would like to see it stay on the minimum ISO setting unless the flash is not capable of supplying enough light to stay there. I do not like the fact that the ISO automatically goes 4x base just to start.

I bought a D5000 last year and because of this behaviour, returned it right away. I keep shooting with my D50 (I really like it; after the affair with D5000 I felt like I was cheating on my girlfriend).

I plan to upgrade to a used D90 (that has normal Auto ISO behaviour) someday.

I’m happy to see other people that share my though about this auto iso/flash problem.
I already wrote to nikon about this; I think everyone concerned with this problem should write to nikon.
They can change this strange behaviour with a firmware. But we’re not enough people complaining about this “feature”.

Hi guys, I just come across this post while doing some research about Nikon flashes. I myself owned a D40 and now using a D7000. I love the D7000 so much that I think it is the best DX DSLR. I have loved and used the Auto ISO feature on my D40 and noticed the different behavior with flash between D40 and D7000 before I made the decision of buying my D7000. I think this is the right move (a very smart one) that Nikon has made with their cameras. Why? I think this move solve a problem that I had when using D40 with flash. Whenever I turned on the flash (usually for taking photos of people against a dark background), the camera stayed at 1/60 and ISO 200 (the minimum ISO for D40) and even with my maximum Aperture at 2.8, I still got a very dark background and a very bright subject. I usually had to switch to M mode to dial in the shutter speed and raised the ISO manually to get my intended exposure. I think that the author of this post is well aware of this problem on old camera system. Switching to Slow sync doesn’t solve the problem because the shutter speed would be too slow but the iso will stay the same. I’m now very happy with the behavior of the D7000, I can set the slowest shutter speed to be 1/30 and the auto iso works exactly as I want it to do. It is not the same as the slow sync setting cause the shutter speed will stay at 1/30 (or any slowest shutter speed that you set). About the behavior with SB600, it is likely because your SB600 was on the TTL-BL mode (BL stands for Balance Light, I guess). I set mine to the TTL (without BL) and it worked exactly the same, though I had to dial it down to -1.0 to get the exposure I want.

To me, this change is a welcome improvement, but Nikon should add an option to enable or disable it in the menu, something like “Auto ISO with flash (ON/OFF)”, just like Ken Rockwell suggested the “Auto ISO in Manual Mode (ON/OFF)”. That would be the best for everyone.

Thanks for the comment, Cuong! Yes my SB-600 was in BL mode, and I didn’t test in “regular” TTL mode.

I agree that this new behaviour will result in more beautiful photographs for many people – especially people who don’t understand the camera. But I still don’t like how they sneaked it in without explaining it properly.

Personally I’d prefer manually cranking up the ISO (like I had to with my D80) than to disable Auto-ISO whenever I want to keep the ISO in check. An underexposed background one sees immediately, whereas a too-high ISO value can go unnoticed until it is too late.

I will post again – I have a few drafts but the last months I have been very busy with other things. I just have to make the time though.

Hey, very nice site. I came across this on Google, and I am stoked that I did. I will definately be coming back here more often. Wish I could add to the conversation and bring a bit more to the table, but am just taking in as much info as I can at the moment.

It’s very nice to find this thread of discussion. However, I think the original post is not completely correct — by my thorough test on my own D7000 with external SB-700 flash. Yes, the camera does automatically select (and display) ISO400 when you set Auto-ISO “ON” and set the ISO to 100 — so the camera indeed chooses 4Xminimum ISO you set when enabled with an external flash. However, this is just what is “displayed”, not what will be “used”! I tried to fire several pictures with Auto-ISO ON and external flash SB-700, and found that the actually ISO used for the photos is 100, 140, 180, 200 or something else, but never exceeds ISO-400!! So the 4X minimum ISO setting is just the maximum ISO the camera will try (before using AUTO FP I think). The camera must have a optimal range of flash power output (in contrast to we believe the camera should try to use as much power as possible) before raising the ISO level. This could balance between the high-ISO noise and flash output, to keep the temperature low and make the recharging fast enough. I think this setting of D7000 is quite reasonable, and I think I will trust the Auto-ISO, even if using an external flash with it!!

Hi Qi!
I verified that my D7000 does USE 4x the set ISO under the conditions I wrote about in my blog (both TTL and TTL-BL on the SB-600). I don’t have a SB-700 to test with but it will be very strange if there is a difference between SB-600 and SB-700 in this regard since both support the same TTL modes. The camera will use a lower ISO if the ambient light is very strong (so strong that it wouldn’t have needed higher ISO without flash either) but I still think my findings are correct (based on my experiment).

I agree that for some cases there are advantages to using higher ISO with lower flash output. I still believe that this should be an option, not forced on users in such a difficult to understand way.

I want to address the problem differently. In my D3100 when I use the internal flash with the Auto ISO set with maximum ISO and min, shutter speed, there is no much problems. But, when I put the SB-400 external flash, in A mood, the ISO falls direclty and consistently giving even underexposure pictures!
So, I noticed it will stick to the MAXIMUM 4x basic ISO setting, regardless the maximum setting, while I wanted higher ISO?!
Any working around this?

Just to clarify – you set Auto-ISO ‘on’ with e.g. max ISO 1600 and min shutter 1/30, with ISO set to 100. Then if you use the built-in flash it will raise ISO to e.g. 1600 (depending on the lighting situation), but the moment you put the SB-400 on the camera it will drop to ISO 400? But as I understand in this case you want the camera to stick to ISO1600 because your SB-400 is not powerful enough to light the scene at ISO400?

If you set the ISO to 1600 then it should not drop below this value, so this should be one way to achieve the desired result.

The example you mentioned is completely correct. And yes I know you are right in your solution.
It’s just the idea of setting it and forgetting about it giving the camera the chance to work its algorithm within the limit you put.
But one time, with the external flash, it puts a maximum for ISO while end result is underexposure. and on the other hand without it, the camera uses the upper limit even if there is still a chance to open the aperture!
I found that it’s known for some other poeple and yes the solution you mentioned of just setting your ISO as you want might be safer, just remember to put it back :)
Many thanks!!

I have the same on d5100. I use A, S, M modes to shot my pictures with built in flash in order to choose my favourite time/aperture/ISO. However, I am very unhappy of this camera behaviour. P mode apparently works in this case worse than the auto mode. To me this odd behaviour appears to be a bug!

In my opinion, the ideal situation is:
In aperture priority, ISO is calculated based on the ambient light alone.
In manual mode, ISO is chosen as low as possible while still obtaining a proper flash exposure.
Off camera flash should behave the same as it does when the external flash is mounted on the hotshoe for a given exposure mode.

It’s not that I didn’t read your post, but the experiments you tried, or at least the pictures you took were using Program and Auto modes.

Thanks so much for this post! I thought I was going crazy! I have been trying to use a f/1.8 aperture indoors for my toddler with high shutter speed and fill flash and the camera blows up the ISO to 1600+. I’m going to have to set a User preset or something and forget about Auto-ISO when I use a flash, but I like to use flash for all different kinds of things and am going to hate tweaking the ISO around all the time :-(

Since my D90 got stolen I rented a D7000 for a few days and I already suffered from this “feature”. I tested this at a restaurant.
All conditions being the same except for Internal flash, without it photos were taken with ~2000 iso. When I opene the flash sensitivity shot to the maximum of 6400. How can this not be a bug? What logic states that the same picture with flash gets taken with a higher sensitivity than that with the flash turned off?
That makes absolutely no sense to me. I’m contemplating not getting the D7000 because of it.

I guess that could happen. When the flash is on the shutter speed is set at 1/60 sec (can be altered on D7000 I believe) in P and A mode. When the flash is off the shutter speed could well be lower ( e.g. 1/30 or 1/15sec in P mode if auto ISO is set to suit). The ISO will then adjust to keep the ambient exposure correct with max aperture in each case.

I have a D40 and wondered about a D5100 mainly to get better high ISO performance (I don’t need more resolution). Now I’m rather put off, especially since with the built-in flash the D40 gives about 58% more fill distance range in bright sunlight due to the high sync speed.

The difference in behaviour between built-in and external flash is quite absurd even if the automatic raising of ISO to match ambient light may have some merit.

[…] driven by algorithms you cannot understand. A much longer argument about “new i-TTL” is made in this blog post. Thus, for example, owners of the D300s find themselves with a completely different i-TTL than […]

The problem of raising the ISO to max auto iso value when using the built-in flash is what bothers me most with my D7000! I think this behavior should be treated as a bug in D7000 and fixed with a firmware update. I understand the reason for implementing it in lower-end cameras (3100 etc.), but not in the enthusiast level camera. Coming from D90 where this awkward logic was not present, I started shooting D7000 the same way and it has ruined many of my shots at the beginning and it still bothers me very much that I have to switch off the auto ISO anytime I use internal flash… I don’t want ISO 3200 with flash, this is stupid.

I believe the Auto ISO could also be improved for non-flash shots. I would like to enter a maximum aperture as well as a minimum shutter speed. Then aperture could be decreased when above threshhold light levels, in parallel with increasing shutter speed.

If you want your D5100 (or d5000, d3100 etc) to sync at 1/200 and a set iso:The workaround is that you set your minimum iso and maximum iso to the same value. I.e.: 400 min & 400 max. Then set your auto iso to allow for 1/200 or whatever other value (as long you don’t exceed the 200 in flashmode). Then, even in P or A-mode the 1/200 (or other settings) is being used :) And you’re iso is set. If it is set to iso400, it’ll snap at iso400. You can set any value you’d like this way. It’s a workaround, but it works. Happy shooting!

Hi all,
I have found a workaround with my D5000: Menu/Custom Settings/Bracketing/Flash: set to Manual, 1/4 power with the built-in flash, and the Auto iso behaves like that of my D40.
With the SB400 external flash, repeat above and set to 1/8 power. The same as my D40.

I finally bought a D7000 after waiting for the new D7100 and deciding that for me it was not worth the extra money. I find the auto ISO to be worse than that on my D40 for the reasons above but also there is another difference. On the D40 if the auto ISO was set to, say, 800 max then it was still possible to set 1600 manually for a short period without having to turn auto ISO off. On the D7000 that is not possible; the camera shows the new higher ISO in the display but take no notice of it.

I have gven up on auto ISO for most purposes. I’ve set the camera to ‘easy ISO’ with ISO displayed in the viewfinder and set the camera so that the main command dial controls aperture in A mode (just like the D40, D3100 etc.). Now in all modes except M the sub-command dial controls ISO and the command dial controls the other variable (flexible program, aperture or shutter speed). The viewfinder shows all the main exposure variables:- shutter speed, aperture and ISO all in a row. This seems much better to me. I do have the U1 preset set to P mode, auto ISO, min speed 1/250, max ISO 6400 so that I can qucikly grab a photograph without taking time to set anything at all.

I have a D7000 with the SB700 flash and only switched it to Auto ISO recently. With min ISO 100 I noticed it was choosing 400 iso with flash on. What concerned me though was the exposure meter in the viewfinder is showing full underexposure, but when photo is taken it looks fine. Do you ignore the exposure meter or correct ISO to a higher setting to centre the exposure meter to 0?

Foxy,
The underexposure reading in the viewfinder is because the background is going to be underexposed. Assuming you are in mode A or P that is probably because the camera is choosing the slowest shutter speed allowed for flash (1/60 by default) and the aperture is not wide enough at 400 ISO. I usually ignore such a reading (on my D40) since the flash usually illuminates the ‘main subject’ OK. What happens with the D7000 built-in flash is that the ISO is allowed to rise to (say) 6400 ISO rather than just 400. This often results in the background being more correctly exposed but allows a loss in image quality. In your case if you want the background exposed better you can select slow speed flash or reduce the slowest shutter speed with flash using custom setting e2. If you are using mode S you can of course slow the shutter speed to allow the background to be correctly exposed.

Thank you for explaining the faulty Auto-ISO with external flash (SB600 in my case). I used to use D70 with the same setting. It was very logical and always produced nice pictures. Now, D7000 often picks ridiculous high ISO (1600) unless I turn off auto ISO.

Hi Kevin
Are you using TTL-enabled wireless triggers? If not, then you have to rely on manual settings anyway. For this kind of work, where you are probably working with a model, and the lighting stays rather static, I would use manual ISO.
Just to be clear: the auto iso is usable the way Nikon implemented it; it may just cause you to use higher ISO than you intended or wanted.
Regards
Francois

I have been accustomed to using Nikon wireless remote flashes for years. D7000 and D7100.
In both of these cameras, I shot macro. Auto ISO set to minimum 100 and maximum 3200 and auto ISO turned ON. I shot in aperture priority mode typically f16 or f22 and used the camera to command two sb-r200 flashes in two groups, the A group in TTL, the B group in TTL -0.3.
The result was that I would consistently get properly exposed photos with varying ISO values within the auto ISO range set in the shooting menu of the SLR.
The camera and flashes would automatically adjust the ISO to obtain proper exposure.
The problem I am having now is that I’ve purchased the D750, and this camera is NOT behaving in a similar fashion. This camera is ignoring the auto ISO settings when using off camera wireless flash, and reverting to the minimum ISO.

My D7100 goes skyhigh in ISO when bouncing with a SB600 in Auto-ISO (base100, max 6400) : on average up to ISO2800.
Note that the Flash HAS enough power (checked by setting flash to 1/1 iso TTL, icm manual A+S and ISO
So, the D7100 prefers raising ISO while limiting flash-power, and using just enough to overpower ambientlight.
So my workaround: fire a 1/1 strobe at ISO100fixed (bounced if needed), and check how many stops the flash underexposes: raise ISO appropriate according to the underexposure the flash is erroring.
e.g. -2 stops -> raise ISO to 400
Next turn auto-iso on again at base100 but LIMIT the max ISO just above at e.g. 640
Nikon should give the user the option to prioritize flash versus ISO-raising (in grades.)

I just upgraded to a d3300 from a d40x, and the whole flash works differently. There’s the high iso problem mentioned. Also with TTL flash, just changing the aperture will change the whole exposure and the flash won’t compensate. It used to be automatic on the d40x. I would shoot outside all day in aperture priority mode, then come inside and just raise the flash and continue shooting, and exposure was fine. Not now. The new flash is a major bug IMO. Can’t see how Nikon can justify it.